(1) Field of the Invention
The present invention relates to a broadcast system having a transmission apparatus and receiving apparatuses, specifically to improvements in digital broadcast services.
(2) Description of the Related Art
In recent years, the infrastructure for the shift from analog broadcasting to digital broadcasting has been improved steadily. In this improvement of the infrastructure, it is important to fully recognize the differences between the analog broadcasting and the digital broadcasting. One of such differences is observed when a transmission path failure occurs.
In the analog broadcasting, when a transmission path failure occurs, the failure is recognized by the audiences as deteriorated reproduction quality. Experiencing more than 50 years of operation of analog broadcasting, the audiences are familiar with such deteriorated reproduction quality that is caused by a thunderstorm or the like.
On the other hand, in digital broadcasting, a transmission path failure causes receiving apparatuses to detect a bit error. When they detect a bit error in a received broadcast wave, the receiving apparatuses correct the bit error using Reed-Solomon parity codes or the like before supplying reproduction output. With these operations, the audiences are supplied with reproduction outputs not deteriorated by the bit error. However, the receiving apparatuses stop supplying the reproduction outputs if a thunderstorm or the like causes a large amount of bit error that cannot be corrected by a bit error correction. It should be noted here that in the present document, a “digital broadcast failure” indicates a large failure that cannot be overcome by a bit error correction.
Meanwhile, the common knowledge: “when a transmission path failure occurs, the failure is recognized by the audiences as deteriorated reproduction quality” may become an unexpected obstacle in digital broadcasting. That is to say, for example, if a sudden thunderstorm occurs while a user is supplied with a reproduction output, the user will probably expect deterioration in the reproduction quality due to the above-mentioned common knowledge that has taken root. However, if supply of reproduction output from a receiving apparatus suddenly stops against this expectation due to a transmission path failure, the user may mistake the transmission path failure for a receiving apparatus failure. In such circumstances, there is a possibility that a flood of complaints about a receiving apparatus failure are sent to the maker of the receiving apparatus each time a thunderstorm or the like causes a lot of transmission path failures. In such a case, the maker will be tied up with dealing with the complaints.